1. Field of the Invention
The invention relates to method and apparatus for providing images of zones of ultraviolet absorbing material in ultraviolet transparent media, such as at least one nucleic acid zone in a gel.
2. Description of the Prior Art
In recent years, there has been a remarkable surge of interest in the study of deoxyribonucleic acid (DNA) molecules. A significant contributing factor to the increased interest in the study of DNA has been the new and rapidly expanding area of molecular biology and related fields, such as genetic engineering.
In connection with genetic engineering, molecular biology, and other fields in which the DNA molecule is studied and on occasion processed to be either modified or replicated, it is for many purposes extremely important to develop a purified sample of DNA representing a particular segment of a particular DNA molecule. In many contexts, for example, a DNA molecule of interest is "cut" by various chemical or physical processes so that a certain segment of that molecule, which is to be studied or otherwise processed, is isolated. One technique for thus isolating a segment of a cut DNA molecule from the other fragments of that same molecule, out of which the segment of interest has been cut, is to cause the DNA segments to migrate in a gel under the influence of an electric field. This technique of electrophoresis causes the migration of different shaped and sized DNA segments to occur at different rates so that at any particular time, the different segments of the DNA molecule involved in the process are at different locations along the path taken by the DNA segments under the influence of the electric field. Such separation of DNA segments if properly conducted results in virtually pure samples of the various separate segments of the DNA molecule which has been severed.
In the context of the electrophoretic separation of segments of a severed DNA molecule, it is crucial to be able to determine the exact location of the DNA segments so that the segment which is of interest can be removed from the gel for further study or other processing. A conventional technique for thus locating a DNA segment of interest is one which involves staining the gel with a compound known as ethidium bromide, illuminating the gel with ultraviolet light, and photographing the pattern with a camera. The ethidium bromide, when locked onto the DNA molecule and illuminated with ultraviolet light, fluoresces, and the fluorescent pattern is then photographed; however, this process has significant drawbacks. Ethidium bromide is carcinogenic and can damage the DNA. In addition, the process requires as much as an hour to complete and necessitates the use of a camera. Also required is a destaining process, whereby the stain is removed from the DNA once the latter is removed from the gel. This leads to additional danger of contamination of workers by the ethidium bromide and additional consumption of time.
Consequently, there has been a felt but unfulfilled need for a system and method for providing images of DNA segments and nucleic acid in gels, which would present no health hazard to the operator and would be expeditious and economical.